Study On Spreading Codes Construction, Selection And Enhanced Reception For Satellite Navigation Signal

Global Navigation Satellite Systems can pr ovide all tim e, all weather and high accuracy positioning, navigation an d timing services to infinite users. GNSS becom es a critical infrastructure of modern country and military power. Signal structure is one of five critical challenges for the success of satell ite navigation s ystem. Signal structu re with compatibility and interoperability,independent intelligence property,high performance is essential for BDS to participate in the global competition of GNSS. This dissertation study on the basic com ponent of CDMA signal structure—spreading code design and enhanced reception of navigation signal. The perform ance metric,construction method,selection method,assignment method and signal-structure-based enhanced reception are addressed in this dissertation. The research results in the full capacity of spreading code design, evaluation and application. The new m ethods are used in the design of BDS OS signal structures and enhanced reception of BD S OS signal. The m ain contributions and innovations of the dissertation are listed as follows.1. A general framework for spreading code design and evaluation and three principles are proposed. The constraints of spreading co de design are analyzed under the view of comm unication, ranging, anti-jamm ing, countermeasure of security and intelligence property. Based on the integra tion of existing rese arch and th e practice of spreading codes design, general fram ework and principle for spreading code design are proposed. In the fram ework, spreading code de signs consist of four basic problem s. The framework guides the decom position and inte gration of spreadin g code project. The framework builds a baseline for the evaluation of code schemes and design m ethods also. The process of spreading code design should follows three principle: limited goals,Divide and Conquer,independent design and evaluation.2. Two spreading code construction methods with length flexibility and high performance are proposed:iteration interleaving code and true random number code. The construction m ethods are designed to meet compatibility and interoperability,independent intelligence property,high performance requirements of BDS spreading codes. Iteration interleaving code bases on perm utation group theory and is generated by using interleaver and feedback-iterate loop structure. A non-period and unpredictable true random number sequence results in true random number code by segmenting and transforming. The new methods could produce flexible-length and high performance spreading codes for any navigation signal and spread spectrum signal. The evaluation under four dif ferent code length shows that the performance of new code families is equivalent or b etter than spreading codes of GPS, Galileo and BDS. The new generators provide candidates for BDS open service signal.3. Two spreading code selection methods with polynomial time and high performance are proposed:Greedy algorithm and Maximum Clique model algorithm. The complexity of spreading c ode selection is quantitative pr ofiled. It is proved that the optimization of combination metric such as cros s correlation function is the source o f NP complexity. An optim ization route is sugges ted based on Divide and Conquer strategy. Greedy algorithm and Maximum Clique model algorithm are proposed to optim ize cross correlation function of spreading codes. Greed y algorithm optimizes the cross correlation function of spreading codes by deleting codes based greedy criterion and is a subtraction strategy. The graph theory is us ed to descript the cross correlation of spreading codes in Maximum Clique model algorithm. The Maximum Clique model algorithm transforms the optimization problem into ite ration searching of Maxi mum Cliques and is an addition strategy. The new algorithm s are polynomial time complexity and fit f or any code length and any co de set size. The re sult of four typical codes optimization shows th at the optimized code sets have better performance than ICD codes under the same code candidate sets.4. New signal structure is designed for BDS uplink signal and a satellite-pair-based method for spreading codes assignment is proposed. To control and command the navigation satellite s of BDS in safety, security and efficient, a new two-channel-and-three-mode signal structure is proposed and th e detail designs are given. The new s preading code schem e has significant im provements in anti-jamm ing and correlation performance. A satellite-pair-based method for spreading codes assignment is proposed by using the inform ation of satell ites constellation and dif ference of cross correlation. The concept of satell ite-pair without interference is given. The re sult of new method on BDS shows that 27 MEO satellite s require only 15 spreading codes without increasing interference. The correlation of up link spreading codes obtains an im provement of 0.3 to 0.55 dB and BDS B1 I spreading code s obtain an improvement of 1.02 to 1.74 dB. The time of spreading codes searching in navigation receiver reduces 44%.5. Two low complexity and near optimal decoding algorithms of BCH code for enhancing BDS open service are proposed. Through the analysis of relation between receiver sensitivity and signal s tructure, it is pr oved that the error correcting algorithm of BCH code in BDS ICD fails to improve navigation receiver performance. Two near optimal algorithm for BCH de coding are proposed to enhance B DS navigation receiver. Low complexity Chase algorithm reduces 60% co mputation of basic Chase algorithm by optimizing syndrome computation and decision metric. Syndrome-assisted list decoding algorithm is an integration of hard decoding and soft decoding. The Syndrome-assisted list decoding algorithm does not need sort operation and has lower com plexity than Chase algorithm. The distance of SNR between proposed algorithms and Ma ximum-Likelihood decoding is less than 0.01 dB and 0.08 dB at BER of 10-5.